Initiative 1639 — approved in November — raises the age to purchase a semi-automatic rifle from 18 to 21, calls for enhanced background checks, and requires buyers to complete a firearm safety course. The initiative also holds gun owners accountable if someone uses their firearm to harm themselves or others.

The National Rifle Association and the Second Amendment Foundation have filed a joint lawsuit challenging the initiative.

"We are aware of this situation and are actively monitoring developments as they occur. Attorney General Ferguson has been clear that he is committed to protecting the legal and constitutional rights of Washingtonians, and upholding the will of the state’s voters in passing Initiative 1639. You can learn more about Initiative 1639 and the role of the Attorney General in the implementation of the new law on our website here. Our office is confident that Initiative 1639 is constitutional, and we intend to defend it in court," Kate Kelly, Policy Director for the Attorney General's office, said in a statement.